Download (direct link):
• ATMARPjequesf. An ATMARP client sends an ATMARP request to the ATMARP server to obtain the ATM address of a destination ATMARP client. The message contains the client’s IP and ATM addresses, and the IP address of the destination client.
• ATMARP reply. This message is used by the ATMARP server to respond to an ATMARP request with the requested ATM address. It contains the IP and ATM addresses of both the requesting and the destination clients.
• ATMARP NAK: Negative response issued by the ATMARP server to an ATMARP_ request.
• InATMARP request: Used to request the IP address of a destination. The message contains the sender’s IP and ATM addresses and the destination’s ATM address.
• InATMARP reply. This is the response to an InATMARP request with the destination’s IP address. It contains the IP and ATM addresses of both the sender and the destination.
An ATMARP client must first register its IP and ATM addresses with the ATMARP server. To do this, the ATMARP protocol must be invoked as follows. Each ATMARP client is
configured with the ATM address of the ATMARP server. After the client establishes a connection to the ATMARP server, it transmits an ATMARPrequest on that connection. In the message, it provides its own IP and ATM addresses and it requests the ATM address of itself by providing its own IP address as the destination IP address. The ATMARP server checks against duplicate entries in its table, time stamps the entry, and adds it to its table. It confirms the registration of the ATMARP client by sending an ATMARPreply. If a client has more than one IP address within the LIS, then it has to register each IP address with the ATMARP server.
Entries in the table of the ATMARP server are valid for a minimum of 20 minutes. If an entry ages beyond 20 minutes without being updated (refreshed), then the entry is removed from the table. Each ATMARP client is responsible for updating its entry in the ATMARP server’s table at least every fifteen minutes. To do this, the same procedure for registering with the ATMARP server is used. That is, the ATMARP client sends an ATMARP request to the ATMARP server with the destination IP address set to its own IP address. The ATMARP server updates the entry and confirms it by responding with an ATMARP reply.
Let us assume that ATMARP client 1 wants to communicate with ATMARP client 2. Assume too that both clients are in the same LIS. If there is already an established connection between the two clients, traffic can flow immediately. Otherwise, a connection can be set up if client 1 knows the ATM address of the destination client 2. If its destination ATM address is not known, client 1 sends an ATMARP request to the ATMARP server. If the server has the requested address in its table, it returns an ATMARP reply. Otherwise, it returns an ATMARP NAK. Upon receipt of the ATMARP reply, a connection is established and traffic starts flowing.
An ATMARP client creates an entry in its ATMARP table for every connection (PVCs or SVCs) that it creates. An entry is valid for a maximum of fifteen minutes. When an entry has aged, the client must update it. If there is no open connection associated with the entry, then the entry is deleted. If the entry is associated with an open connection, then the client must update the entry prior to using the connection to transmit data. In the case of a PVC, the client transmits an InATMARP request and updates the entry on receipt of the InATMARP reply. In the case of an SVC, it transmits an ATMARP request to the ATMARP server, and updates the entry on receipt of the ATMARP reply.
An ATMARP client is also permitted to initiate the above procedure for updating an entry in the table, before the entry has aged.
1. Why is there error control for the header and not for the payload of an ATM cell?
2. How long does it take to transmit an ATM cell over a link, when the link is:
a) a T1 line?
b) an OC-3?
c) an OC-12?
d) an OC-24?
e) an OC-48?
3. Consider the HEC mechanism. Let p be the probability that a bit is received in error.
a) With what probability a cell is rejected when the HEC state machine is in the correction mode?
b) With what probability a cell is rejected when the HEC state machine is in the detection mode?
c) Assume that the HEC state machine is in the correction mode. What is the probability that n successive cells (where n > 1) will be rejected?
d) Assume that the HEC state machine is in the correction mode. What is the probability p(n) that n successive cells will be accepted, where n > 1? (Hint: Write down the expression for p(1) and p(2), and express p(3) as a function of p(1) and p(2). Then write down the general expression for p(n) for any n as a function of p(n — 1) and p(n — 2).)
4. Consider the case of an application running over an ATM network. Assume that each packet generated by the application is carried by n ATM cells, which are transmitted back-to-back. The time to transmit a cell is T and the average time it takes for a cell to traverse the ATM network and reach the destination is D. When all of the ATM cells belonging to the same packet are received by the destination, their payloads are extracted from the cells and are assembled to the original packet. Subsequently, the CRC operation is carried out on the reassembled packet. If the CRC check is correct, the packet is released to the application. Otherwise, a negative acknowledgment is sent back to the source requesting the retransmission of the entire packet. The time it takes to carry out the CRC check is F, and the time it takes for the negative acknowledgment to reach the source is D. Let p be the probability that the ATM cell is received with erroneous payload.