Protobuf message exchange between plain TCP client & Netty Server using Java

I am trying to create a TCP socket connection between a plain TCP client and Netty Server using Protobuf message exchange format in Java and it does not work. It works when I use Netty Client (instead of TCP client) & Netty Server.

At the Netty Server side, in ServerHandler class, I get the Object "msg" as type "PooledUnsafeDirectByteBuf". Now when I try to convert it to my custom Protobuf object it fails with error - 'java.lang.ClassCastException: class io.netty.buffer.PooledUnsafeDirectByteBuf cannot be cast to class ProtoModel'.

public class ServerHandler extends ChannelInboundHandlerAdapter  {
---
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
--- 

Client Side Code

Socket clientConnection = new Socket("localhost",SERVER_PORT);
ObjectOutputStream outToServer = new ObjectOutputStream(clientConnection.getOutputStream());
ProtoModel.writeTo(outToServer); //ProtoModel is the protobuf class

I think it is something to do with Protobuf message encoding at TCP client end and decoding at Netty Server end. The same server code works when I use a Netty Client (as opposed to plain TCP Client).

Netty Client Code

EventLoopGroup group = new NioEventLoopGroup();
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group).channel(NioSocketChannel.class).handler(new ClientInitializer());
Channel ch = bootstrap.connect("localhost",SERVER_PORT).sync().channel();
ChannelFuture lastWriteFuture = ch.writeAndFlush(ProtoModel);
lastWriteFuture.channel().closeFuture().sync();

Please let me know if any other input is required from my end. Many thanks.