Layer-3 Switch for remote access

In a star wide area network topology that is centered at one end and connected to hundreds of nodes through digital channels, if you use the traditional network connection mode, the limited processing capability and high availability of network devices are two major factors restricting technical solutions. With the launch of a new generation of broadband access technology and equipment, new network connection solutions are also coming soon.

The new network access solution is to use the core switch supporting layer-3 VLAN) technology to replace the traditional router as the WAN connection device, through the digital leased line channel at both ends of the support for G.703-ETH conversion Ethernet Bridge access, the Wan digital channel is transparently transmitted between two local networks, and a vlan id and an IP address segment are allocated to each branch node in the center.

In recent years, VLAN technology and the development of layer-3 Switch Equipment mature, supporting G.703-ETH Switch Ethernet bridge equipment is also widely used, which opens up a broad prospect for the development of network technology. Currently, layer-3 switches are widely used in LAN of buildings and campuses, and Ethernet bridges are only used to extend the distance of LAN, the combination of the two new technologies for large-scale use in the star wide area network topology requires constant exploration and improvement in practice.
VLAN Technology

In 1995, various exciting new LAN technologies began to be applied. The technologies that have received great attention are those based on switching, especially switching Ethernet, fast Ethernet, and ATM technologies. One of the first benefits of these technologies is VLAN, which has the following features:

1) easy to change and move devices on an IP Network
In traditional local area networks, network administrators spend a lot of time processing device movements and changes. If a VLAN is installed, you only need to change the software configuration without the need for mobile devices.

2) Additional security
The device in a VLAN can only communicate with the device in the same VLAN. If the device communicates across VLANs, the data information must pass through the routing device or support layer-3 switches.

3) more effective control of broadcast traffic
In traditional local area networks, broadcast traffic may cause congestion because data is sent to all devices, whether or not they need it. VLAN can improve network efficiency and set the devices that need to communicate in the same VLAN.

4) reduce routing requirements
VLAN routing in a layer-3 switch is characterized by a single route and a route everywhere. This will greatly reduce the routing dependency of data transmission.

5) supports multimedia applications and efficient multicast control

Communication access device
In recent years, the G.703-ETH Ethernet bridge is very suitable for the above-mentioned communication access equipment, it has the following features:
1) G.703 lines support a distance of up to 1 km;
2) the clock can be set to an internal clock, line clock, or an external clock;
3) It has two plug-in and stand-alone structures. The plug-in type can be inserted into the 19 inch chassis with 14 slots. It is very suitable for centralized management in the central data center and the stand-alone type can be used for branch nodes;
4) Ethernet interfaces include UTP10BaseT/100 BaseT and BNC10Base2. Up to 10000 LAN table addresses can be entered;
5) the speed of filtering and forwarding reaches 15000 frames per second, the buffer can accommodate 200 frames, and the throughput wait is 1 frame;
6) supports IEEE 802.1/Q, that is, VLAN frame extension (optional ).

The Ethernet interfaces of such devices are also modular and can be inserted into the V.35 module and connected to the vro as needed. They comply with the IEEE 802.3/Ethernet standard and can also meet network design requirements, choose a module that supports IEEE 802.1/Q. This device has high flexibility and practicality.

Comparison between vrouters and layer-3 vswitches
As we all know, vrouters are expensive compared with hubs and vswitches, and low-end routers do not support direct access to G.703, and G/V converter equipment must be used. In the branch node, generally do not configure high-end router, even the low-end router is much more expensive than the hub or switch, and the use of G.703-ETH bridge converter for access, the price is equivalent to G/V converter, therefore, with the new network access solution, the larger the scale, the more nodes that are connected to the downlink, the more cost savings.

When the center end of the uplink uses a layer-3 Switch for access, the downlink branch node does not need any grade router, only need to be equipped with a hub or switch and G.703-ETH bridge converter, about 10 thousand yuan.

1. Port density and scalability
No matter which manufacturer or vro you are using, there is a limit on the number of access requests. Taking the Cisco 7513 vro as an example, this is currently the industry's maximum E1 port density of only 168 devices. You can only use the second router to expand the number of ports. However, when using a vswitch, there is no limit on the number of connections. Taking Cisco Catalyst 6509 as an example, although its 10/100 M port density can reach 336, however, for more accesses, you can expand the number of switches that support L2 VLAN Through cascade. This quantity is unlimited.

A vlan id can be assigned to each branch node during solution design. Cisco Catalyst 6509 has 1000 identifiers available for allocation. When there are more than 1000 branch nodes, allows two nodes with small data volumes to share a vlan id.

2. Data processing capability
Generally, the packet forwarding rate of A vro is several hundred kpps and the bus bandwidth is 2 Gbps. The packet forwarding rate of A vswitch can reach over mpps, And the backboard bandwidth can be up to 32 Gbps. It can be seen that the data processing capability of a layer-3 switch is much higher than that of a router.

3. Protocol Support
Like routers, layer-3 switches support network protocols such as IP, IPX, and DECnet, as well as open dynamic routing protocols such as RIP and OSPF. To put it simply, in common cases, most of the Protocol vswitches supported by the vro can be implemented, while some functional vrouters unique to the vswitch cannot be implemented.

4. Analog channel, X.25, and Frame Relay
The analog channel can only communicate at a low speed. It must be modulated and demodulated by the band Modem, and no access device is required to convert it to Ethernet. X.25 and Frame Relay are both point-to-point connections, not leased line networks, vswitches cannot support these connections before the vro completes. However, some high-end core switches, such as Cisco Catalyst 6509, can connect to a wide area network module to implement all the functions that the router can accomplish.

5. Support for redundant channels
When the redundant channel is the same digital channel, the switch has a unique function: to combine two or more identical physical links into one logical link, accumulating bandwidth, as long as one of the links is good, the connectivity can be maintained. The device of the 3Com function is defined as Trunk, and the Cisco device is defined as Channel. Similar principles are implemented at the physical link layer.

When a redundant channel is a digital channel and a simulated channel coexist, a router must be used. To avoid dynamic Routing occupying the WAN bandwidth, HSRP (Hot Standby Routing Protocol) can be selected on the branch node based on different products) or VRRP (Virtual Routing Protocol) Protocol, in the central end, you can use RIP or OSPF Dynamic Routing Protocol in the LAN to exchange Routing information between the Router and the switch. If you use a core switch with a WAN module slot, you can complete dynamic routing information exchange.

6. Price-Performance Ratio
The performance and price of a router and a vswitch are incomparable because the vro is a WAN device and the vswitch is a LAN device. However, after a layer-3 switch is used to replace the router access scheme, this comparison is required.

A vro with a certain number of E1 port access costs RMB 100,000, while a low-end switch with a support of three layers costs less than RMB 100,000, and a high-end core switch only needs RMB 100,000, depending on your needs, the configuration is also different. The cost of a vswitch and a vro port is 10 times different, and the processing capacity is dozens times higher. Such a high performance and price difference provides an important basis for the new network access solution.