Basic knowledge and application of E1/T1 Communication

Source: Internet
Author: User

E1 introduction:

① An E1 is a 2.048m link, which is PCM encoded. ② The frame length of an E1 is 256 bits, which are divided into 32 time slots and 8 bit for a single time slot. ③ 8 K E1 frames per second pass through the interface, that is, 8 K * 256 = 2048 Kbps. ④ Each time slot occupies 8 bits in the E1 frame, 8*8 K = 64 K, that is, an E1 contains 3

2 64 K.

E1 Frame Structure

E1 can be divided into three methods: frame formation, Compound Frame formation, and non-frame formation. In E1, 0th time slots are used to transmit Frame Synchronization data, and the remaining 31 time slots can be used to transmit valid data; in the E1 of the Compound Frame, except for the 0th time slot, the 16th time slot is used for transmission signaling, and only 30 time slots from 1st to 15, 17th to 31st can be used for transmission of valid data; in the case of no frame E1, all 32 time slots can be used to transmit valid data.


Frame Structure of E1 Channel

In the E1 channel, 8 bits form a time slot (TS). 32 time slots form a frame (f) and 16 frames form a complex frame (MF ). In one frame, ts0 is mainly used to transmit frame location signal (FAS), CRC-4 (Cyclic Redundancy verification) and peer alarm indication, ts16 is mainly used to transmit along-line signaling (CAS) the secondary frame location signal and the secondary frame end alarm indication, ts1 to ts15 and ts17 to ts31 a total of 30 time slots to transmit voice or data and other information. We call ts1 to ts15 and ts17 to ts31 as "Net Load", and ts0 and ts16 as "overhead ". If the out-of-band public channel signaling (CCS) is used, ts16 will lose the purpose of the transport signaling, and the time slot can also be used to transmit information signals. In this case, the Net Load of the frame structure is ts1 to ts31, the overhead is only ts0.


Introduced by PCM code E1:

According to the characteristics of E1 time slot in PCM encoding, E1 is divided into 32 Time Slot TS0-TS31. Each time slot is 64 KB, where ts0 is the frame synchronization code, which is occupied by Si, SA4, sa5, sa6, SA7, and a bits. If the system uses CRC verification, then, the CRC verification code is transferred from the SI bit position. Ts16 is the signaling time slot. When signaling (common or along-line signaling) is used, this time slot is used to transmit signaling, and users cannot transmit data. So there are 2 m PCM code types

Pcm30: pcm30 user available time slot is 30, TS1-TS15, TS17-TS31. Ts16 transmission signaling, no CRC verification.

Pcm31: pcm30 user available time slot for 31, TS1-TS15, TS16-TS31. Ts16 does not transmit signaling or CRC verification.

Pcm30c: pcm30 user available time slot is 30, TS1-TS15, TS17-TS31. Ts16 transmission signaling with CRC verification.

4 pcm31c: pcm30 user available time slot for 31, TS1-TS15, TS16-TS31. Ts16 does not transmit signaling and has CRC verification.

CE1 refers to dividing 2 m transmission into 30 64 K time slots, which are generally written as N * 64. You can use several of these time slots, that is, only use N 64 K, must be connected to CE1/PRI.

CE1 ---- up to 31 channels can carry data timeslots 1----31 timeslots 0 for synchronization.


E1 interface:

G.703 non-balanced 75 ohm, balanced 120 ohm2 Interface


Three methods to use E1: 1. use the entire 2 m as a link, such as DDN 2 m; 2. use 2 m as several 64 K and their combinations, such as 128 K and K. This is CE1; 3. when used as a digital relay for a voice switch, this is also the most original usage of E1, which is to use an E1 as 32 64 K, however, the time slot 0 and time slot 15 are used as signaling, so an E1 can transmit 30 voices. PRI is one of the most commonly used access methods. It is also called the HPA signaling standard.

Use a WAN Interface Card, such as 2611, connected to the E1 line through the V.35-G.703 converter. This cost should be lower than E1 card. At present, the 2 m speed line of DDN is usually pulled to the user side through the HDSL line. E1 can be pulled from the optical fiber from the transmission device to the user-side optical terminal to provide the E1 service.


Precautions for using E1:

When the E1 interface is connected to each other, no signal loss, frame out-of-progress, frame out-of-progress, or slide code alarms are reported for both sides of the E1 interface. However, both sides must be completely consistent with the E1 interface parameters, because of the inconsistency of some characteristic parameters, no alarm is triggered on the indicator or alarm platform, but the data channel may fail, the error code, the slide code, and the error code may fail. These characteristic parameters mainly include impedance/Frame Structure/crc4 verification, and the resistance can be 75ohm or 120ohm, and the frame structure can be pcm31/pcm30/no frame; on the Xinqiao node host, the pcm31 and pcm30 are described as CCS and CAS respectively. During connection, the network administrator must be informed of the selection of CCS and whether CRC verification can be performed flexibly. The key is to ensure consistency between the two parties, this ensures that the physical layer is normal.



  1. Who controls E1 and CE1, telecom or user devices on both sides of the interconnection? The user side must support them and how China Telecom achieves them separately. Answer: first, it is determined by China Telecom. China Telecom can provide both E1 and CE1 lines, but the E1 lines of general users are CE1, unless you only use E1, then it is determined by your device. CE1 can be used as E1, but E1 cannot be used as CE1.
  2. CE1 is available for 32 time slots, right? Answer: The Zero and 16 time slots of CE1 are not used. The zero is the transfer synchronization number. The 16 transfer control command can only use 30 time slots: 1-15, 16-30.
  3. How does E1/CE1/pri differentiate the relationship with 2 m in general. How can I associate it with DDN at 2 m? Answer: Both E1 and CE1 are E1 line standards. PRI is an ISDN main line, namely, 30B + D. 2 m of DDN is a transparent line. You can run any protocol on it. The difference between E1 and CE1 can be divided into time slots.
  4. Relationship between E1/CE1/PRI and signaling and time slot answer: E1, CE1, all are 32 time slots, 30 time slots, 0, 16 send synchronization signals and control signals respectively, PRI uses 30B + D and 30B to transmit data, and D-Channel Transmission signaling. E1 is a CAS structure called in-band signaling. PRI signaling is sent separately from data, that is, out-of-band signaling.
  5. Can CE1 be connected to E1. A: Of course, CE1 and E1 can be interconnected. However, CE1 must be used for E1, that is, it cannot be used by time slot.
  6. To achieve a one-to-multiple-point interconnection using CE1, the center must be 2 m now, and the speed of each branch is N * 64 K <2 M. How can the branches be physically connected? How does China Telecom control the uplink and downlink and separate different locations of the circuit? A: divide the time slot on your device, and divide the same time slot order on the telecom nodes. China Telecom only needs to follow the Time Slot Sequence and the branch location you provided, upload each corresponding time slot to the corresponding pivot point using the DDN line.
  7. Can port CE1 directly connect to the E1 cable and connect to the E1 port of the Peer router? A: No
  8. What is the difference between me1 in Cisco 7000 Series and E1 and CE1 in Cisco 2600/3600? A: me1 on Cisco 7000 can be configured as E1 and CE1, while E1 and CE1 on Cisco 2600/3600 only support their own functions.
  9. What is the difference between non-equilibrium and equilibrium? A: It mainly refers to the electrical difference. The balance refers to the total output of the two output ends, which is 120 Ohm. The two non-balanced output ends have only one output, while the other is grounded. Is 75 ohm non-balanced: the cable on the router end is a DB-15 (male) connector, on the network end is a BNC head balanced: the cable on the router end is a DB-15 (male) connector, on the network side is a RJ-45 Connector


Supplement-optical terminal usage:

Optical fiber --- optical transceiver -- coaxial axis --- g703 to v35 converter -- Synchronous Serial Port


BNC-DB15, BNC-RJ45 --- CE1

CE1/pri Cables

Cisco Systems makes four cables for the CE1/pri modules. All four have DB-15 connectors on the CE1/pri end and either BNC, DB-15, twinax, or RJ-45 connectors on the network end.

The following figures show the CE1/pri interface cables:

Figure 1. E1 interface cable for 75-ohm, unbalanced connections with BNC connectors


Figure 2. E1 interface cable for 120-ohm, balanced connections with DB-15 connectors


Figure 3. E1 interface cable for 120-ohm, balanced connections with twinax connectors


Figure 4. E1 interface cable for 120-ohm, balanced connections with an RJ-45 Connector


II,2 m usage.


1. Applications on the switch network. (1) At present, the MSC uses a 2 m structure in the pcm31 format. The entire 64 kbit/s time slot within 2 m carries one route .. (2) Currently, the Standby clock of the switching network device is used to extract Frame Synchronization signals with 0 time slots within 2 m. (3) The clock synchronous extraction method of the station is to synchronize the signals between the BSC and BTs using frame synchronous signals with 0 time slots within 2 m. (4) MSC-BSC, BSC-BTS between the interface using the channel rate of 16 kbit/s, 32 kbit/s and other different rates, how is this rate achieved in transmission? The 64 kbit/s channel with 2 m frames is reused and reused. At present, some of our 2 m testing instruments have a interface testing function, it can monitor and monitor the performance of 16 kbit/s and 32 kbit/s.


2. Online Application of signaling. Currently, the entire network in our province uses the No. 7 signaling system. Currently, there are two types of signaling chains: 64 kbit/s signaling links, the other is the 2 mkbit/s Signaling Link. When a 64 kbit/s Signaling Link is used, the frame structure of the 2 m circuit is pcm31, and according to security considerations, within 1 2 m, more than 8 64 kbit/s signaling links cannot be carried. For a 2 mkbit/s Signaling Link, the frame-based pcm31 is also used for transmission, but only for encapsulation at the service layer switch.


3. Data online applications. Currently, the 2 m circuit on the data network uses a non-frame format. However, in actual use, there may be the following misunderstanding: the actual bandwidth of the 2 M data link is 2048bit/s, since data is transmitted asynchronously, zero time slot is not required for synchronization. This recognition is biased. In fact, the actual bandwidth used by the 2 M data link is 1984bit/s, and the 0 time slot within the 2 m is retained. Please pay attention to this.


4. Network Management online applications. Currently, our provincial network management basically uses the pcm31 format for 2 m applications. Due to the low bandwidth requirements of some network management systems, the 64 kbit/s cross device is used to cross the network management time slots of different network management systems to the same 2 m for transmission. However, the current trend of the network management network is to establish a unified large-capacity platform, and then various types of network management are transmitted through this platform in a unified manner, greatly reducing the complexity of the network management network.


5. 2 m testing. 2 m testing is the most important two methods, one is online testing and the other is disconnection testing. (1) In online testing, two receiving ends of the meter are connected to a 2 m circuit with high impedance, the principle of the test code is to check whether the HDB3 code type complies with the HDB3 code encoding rules (that is, four "0" signals cannot be connected). Therefore, according to the principle, the online test tests the code-type error rate, rather than the bit error rate. It can only be used to determine whether the quality of the model is 2 MB or not. to accurately determine the quality level, a disconnection test is required. (2) The main principle of disconnection testing is to connect one end of the loop and the other end to the receiving end and sending end of the instrument, and then send a pseudo-random code through the Instrument for 2 m or 64 K testing, another method is to use both ends of the instrument to send a pseudo-random code, and the other instrument to receive it. This test method has a high accuracy, but requires two high-precision instruments.


2. Introduction to T1

The T1 digital stream consists of 24 64-kbpsChannelS that areMultiplexed. (The standardized 64 Kbps channel is based onBandwidthRequired for a voice conversation .)

In the T1 system, voice or other analog signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. with 24 channels being digitized at the same time, a 192-bitFrame(24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. each frame is separated from the next by a single bit, making a 193-bit block. the 192 bit frame multiplied by 8,000 and the additional 8,000 framing BITs make up the T1's 1.544 Mbps data rate. the signaling bits are the least significant bits in each frame.

Super frame (SF)

Generally, a super frame (SF) consists of 12 frames (or 2316 bits), each of which contains 193 bits.

The extended superframe ESF usually consists of 24 frames (or 4632 bits. Each frame contains 193 digits.


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