Forum of Layer 2 Layer 3 technologies

Packet Over SONET/SDH : Many of us use the POS interfaces in the routers . So here we will have one small technical summary about POS(packet over SONET/SDH) POS also known as PPP over SONET/SDH . This is scheme which uses PPP encapsulation to map IP datagrams into the SONET/SDH payload . Why SONET/SDH payload and PPP are used for enacapsulation : Since SONET/SDH is point to point circuit , PPP is well suited here . POS layers : There are three pos layers. They are 1 . Bottom layer : mapping into SONET/SDH 2 . Mid layer - Framing of PPP with HDLC . 3 . Top layer – IP encapsulation into PPP Here I rememember Sridhar G , my mentor in HCL . I created the stream for POS interface and traffic was not success . At that time , he told me to select the HDLC in Agilent RT. For Ethernet , We use some other encapsulation in RT. Please share that info if u know. Operation of POS is : When transmitting : IP -> PPP->FCS generation->Byte stuffing->scrambling-SONET/SDH framing When rec...

Trace Route Process A . Traceroute sends out 3 ICMP echo packets to the named host, but with a TTL of 1; then with a TTL of 2; then with a TTL of 3 and so on. Traceroute will then get 'TTL expired in transit' message back from routers until the desination host computer finally is reached and it responds with the standard ICMP 'echo reply' packet. Please note that TTL increment happens till destination is reachable or TTL reaches its maximum value. Trace route is mainly used in troubleshooting of the networks Possible ICMP error messages in trace route : H :- Host unreachable. The router has no route to the target system. N :- Network unreachable. P :- Protocol unreachable. S :- Source route failed. You tried to use source routing, but the router is configured to block source-routed packets. F :- Fragmentation needed. This indicates that the router is misconfigured. X :- Communication administrative...

In the early 1980s, the International Standards Organization (ISO) recognized the need for a standard network model. This would help vendors to create interpretable network devices. The Open Systems Interconnection (OSI) reference model, released in 1984, addressed this need. The OSI model describes how information makes its way from application programs through a network medium to another application program in another computer. It divides this one big problem into seven smaller problems. Each of these seven problems is reasonably self-contained and therefore more easily solved without excessive reliance on external information. Each problem is addressed by one of the seven layers of the OSI model. Layers - Functions - Devices The application layer The application layer of the OSI model is the layer...